Methods for fabricating pattern rolls

ABSTRACT

A pattern roll especially adapted to form, in an in-line manner, peripheral edges of an article having substantially constant geometry and the pattern roll&#39;s method of fabrication are described. A bounded surface region is defined on at least a portion of a pattern roll&#39;s cylindrical surface by means of a number of circumferential and longitudinal (relative to the pattern roll&#39;s central axis) segments. Beveled surfaces are formed on these rib segments with the angle formed by the beveled surface of the circumferential segment being less that the angle formed by the beveled surface of the longitudinal segment. Notwithstanding this angular difference as between the beveled surfaces of the circumferential and longitudinal rib segments, when the pattern roll is then rotataed in opposition to a platen roll so as to define a nip therebetween, and a molten thermoplastic is extruded into the defined nip, a plastic product having a peripheral beveled edge of substantially constant geometry will be formed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.07/250,684, filed on Sept. 29, 1988, (now U.S. Pat. No. 4,938,677) whichis a continuation-in-part of U.S. Application Ser. No. 07/017,603 filedon Feb. 24, 1987, entitled "Apparatus Methods for Forming a Pattern on aRoll", and (now abandoned) Ser. No. 07/158,622 filed on Feb. 22, 1988,entitled "Method for the Continuous In-Line Edge Molding of ExtrudedPlastic Products" (now abandoned), the entire content of each of theseapplications being expressly incorporated by reference herein.

FIELD OF THE INVENTION

This invention relates to pattern rolls especially adapted for forming,in a continuous in-line manner, beveled peripheral edges on extrudedplastic products. In specific embodiments, the invention relates topattern rolls and methods of using the same during the simultaneousextrusion and molding of beveled edges of a floor mat (e.g., mats whichare sometimes referred to as "chair mats").

BACKGROUND AND SUMMARY OF THE INVENTION

In the formation of many plastic articles, plastic sheet material isusually passed between die rolls, one or both of which may have apattern negative for producing a pattern on the final sheet plasticproduct. Typically however, the formation of plastic products accordingto these conventional processing techniques depends upon the use ofpreviously formed sheet stock plastic material. While the use ofpreviously formed sheet stock material is typically not objectionablewhen most plastic products are produced, there are some significantdisadvantages when these conventional product-forming techniques areemployed to produce plastic products having contoured (e.g., beveled)peripheral edges.

For example, in the production of floor mats of the type which arecustomarily placed between a chair's legs and the floor's surface so asto protect the latter from the marring effects of the former, it isconventional to first form a sheet of plastic material and then "punchout" (i.e., stamp) individual mats from the previously formed plasticsheet. Obviously, this technique does not lend itself to the formationof contoured or beveled peripheral edges which bound the mat. Instead,when beveled edges are desired, it is customary to employ a router orlike edge-forming tools so as to, in essence, grind, cut or otherwiseshape the mat's edge to the desired contoured configuration. Thisconventional technique, while effective to form contoured edges,sacrifices the visual appearance of the edge (not to mention its laborintensity which contributes to increased costs and/or slower productionrates for such chair mats). Thus, the peripheral edges of mats formed inthis conventional manner usually are marred due to the abrasive effectsof the mechanical router.

The problems mentioned above could be solved by batch molding individualmats using suitably configured molds--i.e., molds which have the desiredcontoured edges of the resulting mat product. However, it is wellrecognized that batch molding of chair mats is a cost-prohibitivesolution and thus, is not viable to mass produce chair mats atreasonable production costs.

It would therefore be desirable if contoured edges could be "molded" ina continuous in-line manner so as to enhance the visual appearance ofthe edges. It would also be very desirable from a production economicpoint of view if such in-line molding could be accomplishedsimultaneously with the extrusion of a thermoplastic material so as toproduce, in a unified step, both the mat (or at least a preform of themat) and the mat's contoured or beveled edges. The methods according tothis invention achieve these desired results.

According to this invention, a plastic product (for example, a chairmat) having continuous contoured (e.g., beveled) peripheral edges may beformed by using a novel pattern roll. An interior region of acylindrical surface portion on the pattern roll is bounded by means of acontinuous "rib" which corresponds to the outline of the mat and alsohas surfaces corresponding to the desired contoured or beveled edge ofthe mat.

A nip is formed between the pattern roll and a platen roll. Uponrelative rotation of the pattern roll in opposition to the platen roll,discrete volumetric portions of the bounded interior region willsequentially continuously be presented to the defined nip.Simultaneously with the rotation of the pattern roll, a moltenthermoplastic material is extruded into the volumetric portions of thebounded interior region which are sequentially continuously beingpresented at the nip. This extrusion/rotation thus causes the moltenthermoplastic material to fill the presented volumetric portions of thebounded region. As may be appreciated, when this technique is practicedon a continuous, in-line manner, the bounded region will eventually forman outline of the plastic product and will, moreover cause thethermoplastic to be flowably compressed in the defined nip. Thiscompression, in turn, allows the contoured edges to, in effect, bemolded for each sequential volumetric presentation of the boundedregion. In other words, the method of the present invention employsthermoplastic extrusion techniques in combination with an in-linemolding technique so as to form a plastic mat, for example, having thecontoured edges.

A plastic product (e.g., a chair mat) is thereby produced with contouredor beveled edges without the need to first form a sheet of plastic stockand then subject the stock to after-treatments such as, cutting, edgeforming and the like. That is, the method of the present inventionproduces contoured or beveled edges on a plastic product simultaneouslywith the formation of the product itself (or at least simultaneouslywith the formation of a product preform).

The novel pattern roll which may be employed in the product-formingmethod described briefly above is fabricated from a cylindrical baseroll and a cylindrical sleeve. Specifically, a recessed groove having atleast some circumferentially and longitudinally (i.e., relative to thebase roll's axis) extending groove sections is formed in the base roll.Corresponding circumferential and longitudinal rib segments are formedfrom the sleeve by removing unwanted regions thereof. Beveled surfacesproviding a negative image of the beveled edge on the article to beproduced are then formed on these circumferential and longitudinal ribsegments.

Important to the present invention is that the beveled surfaces on thecircumferential rib segments are formed at an angle A₁ less than anangle A₂ of the beveled surfaces formed on the longitudinal ribsegments. Notwithstanding this angular difference, a plastic producthaving a peripheral beveled edge of substantially constant geometry maybe formed.

Adjacent ones of the circumferential and longitudinal rib segments maybe joined by means of a radius rib segment which also includes a bevelededge continuous with the beveled edges of the circumferential andlongitudinal rib segments which it joins. However, due to the angulardifference of the beveled edges formed on the circumferential andlongitudinal rib segments, the beveled surface formed on the radius ribsegment presents a smooth angular transition surface between the anglesA₁ and A₂.

Other advantages and aspects of this invention will become more clearafter careful consideration is given to the detailed description of thepreferred exemplary embodiments of the invention which follow.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will hereinafter be made to the accompanying drawings whereinlike reference numerals throughout the various FIGURES denote likestructural elements, and wherein;

FIG. 1 is a schematic perspective view of a chair mat having contourededges produced in accordance with the present invention;

FIG. 2 is a cross-sectional profile of a preferred contoured edge whichmay be produced by the present invention;

FIG. 3 is a schematic diagram showing the various processing stepsemployed in the present invention;

FIG. 4 is a top plan view of a web of mat preforms having contourededges produced by the present invention;

FIG. 5 is a cross-sectional elevational view of the mat preforms shownin FIG. 4 and taken along line 5--5 therein;

FIG. 6 is a side elevational view showing the operative cooperationbetween the pattern roll of this invention and the platen roll;

FIG. 7 is a side elevational view of a preferred pattern roll accordingto this invention;

FIG. 8 is view showing the exterior of the pattern roll of FIG. 7projected onto a planar surface for ease of discussion;

FIG. 9 is a perspective view showing the base roll and the continuouspattern rib in a disassembled condition;

FIG. 10 is a cross-sectional elevational view of the pattern roll astaken along line 10--10 in FIG. 8;

FIG. 11 is detailed schematic cross-sectional view of a longitudinalgroove segment as taken along line 11--11 in FIG. 9;

FIG. 12 is a detailed schematic cross-sectional view of a longitudinalsegment of the continuous pattern rib of this invention as taken alongline 12--12 in FIG. 9;

FIG. 13 is a composite schematic cross-sectional view of thelongitudinal and circumferential pattern segments of this invention;

FIG. 14 is a detailed schematic cross-sectional view of the pattern ribas taken along line 14--14 in FIG. 9;

FIG. 15 is a cross-sectional view of an alternative pattern rib profilewhich may be employed in the pattern roll of this invention; and

FIG. 16 is a cross-sectional view of another alternative pattern ribprofile which may be employed in the pattern roll of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EXEMPLARY EMBODIMENTS

FIGS. 1 and 2 illustrate a representative plastic product which may beproduced in accordance with the present invention. The productillustrated in FIGS. 1 and 2 is in the form of a chair mat 10 having abase 12 and a forward extension 14 for disposition in the well of a deskwhereby a chair, not shown, mounted on rollers and disposed on the uppersurface 16 of mat 10 may be readily and easily moved about the mat. Theperipheral edges of the mat 10 are in the form of a taper which slopesdownwardly and outwardly from the top surface 16 to a marginal terminaledge 19. The tapered edge 18 is, moreover, a substantially constantlength dimension L (as measured in a plane parallel to edge 18) aboutthe entire periphery of mat 10. The taper of edges 18 is present so asto more easily facilitate smooth movement of the chair both onto and offthe mat 10.

A schematic representation of a method in accordance with presentinvention of making the mat 10 is shown in accompanying FIG. 3. As isseen, a suitable thermoplastic material (usually in the form of pellets)is added to the screw extruder 20 via hopper 22. As is well known,extruder 20 thoroughly fluxes and heats the thermoplastic so that it isin a molten form when transferred to the extrusion die 24. The moltenthermoplastic is then extruded from a slit (not shown) of predetermineddimension formed in the die 24 so that the molten thermoplastic isforced into a nip 26 defined between pattern and platen rolls 28, 30,respectively.

As will be described in more detail hereinafter, pattern roll 28establishes a bounded region defined by a continuous pattern rib whichforms the peripheral outline of the mat 10. The rib also includescontoured surfaces which conform to, and thus form, the contoured edge18 of the resulting mat 10. That is, the outline on the pattern roll 28,when projected onto a planar surface, will correspond to the peripheraledge 18 of mat 10.

The platen roll 29 may have a smooth or textured cylindrical surface, orit may be provided with cleat-forming recesses so as to concurrentlyform cleats 31 extending from the bottom surface 17 of the chair mat 10(see FIG. 2). These cleats 31, as is well known, provide a means forpositionally retaining the chair mat 10 against a floor surface.

Since the thermoplastic material exiting die 24 (designated by referencenumber 24a) is in a molten state, it will flow laterally of the rollsunder the compressive forces of the pattern and platen rolls 28, 30, atthe nip 26. Thus, the established region of the pattern roll 28 will befilled with the molten thermoplastic 24a and will exit the nip 26 in theform of a sheet 29. The sheet 29 then passes around an idle roll 32which may be supplied with a cooling medium (e.g., water) so as tosolidify the sheet 29. The sheet 29 then passes on to further downstreamprocessing such as removal of the mat 10 from waste regions of the sheet29 via cutting assembly 50 (to be described below).

As is seen in FIG. 4, a sequential number of mat "preforms" 40 isformed, each preform 40 being defined (i.e. bounded) by a tapered edge18 yet connected to lateral waste regions 42 of sheet 29. These matpreforms 40 may then subsequently be removed thereby forming individualmats 10 by passing the sheet 29 into contact with a cutter roll assembly50 (see FIG. 3). Cutter roll assembly 50 may be comprised of a cutterroll 52 and a pressure roll 54 which is preferably coated with anelastomeric layer. Cutter roll 52 defines a cutting edge correspondingin shape and outline to the peripheral terminal end 19 of edge 18 (seeFIG. 2).

Roll 52 is rotated in synchronism, via synchronizing means 56, with thesequential passage of the mat preforms 40 so that the cutting edges onroll 52 register exactly with an outer plane passing perpendicularlythrough the edges 18 of mat preforms 40. The preforms 40 are thussevered from the waste regions 42 of sheet 29 along planes which areshown by chain lines 54 in FIG. 5 to thereby form the terminal end 19 ofedge 18.

The synchronizing means 56 can be of any suitable type, for example,mechanical synchronizing systems employing a pulley and timing chain.Synchronizing means 56 may also be embodied in the form of amaster/slave electronic and/or pneumatic control system which measuresthe rotation speed of roll 32 and/or rolls 28, 30 for example, and thensynchronizes the rotation of roll 52 to this measured rotation speed.

The pattern and platen rolls 28, 30, respectively, are shown moreclearly in accompanying FIG. 6. Pattern roll 28 includes a continuouspattern rib 60 extending about at least a portion of the pattern roll'scylindrical surface 63 so as to establish an interior region 62 boundedby the pattern rib 60 (and thus recessed relative to the upper region ofthe rib 60) and a lateral (i.e., outside region 62) waste region 65. Asis seen, the rib 60 establishes a planar beveled surface 64 which slopesupwardly and outwardly away from the bounded interior region 62. Surface64 thus presents a negative image of the tapered peripheral edge 18 tobe formed on the mats 10. The pattern roll 28 at each end thereofincludes cylindrical collars 25a and 25b which prevents inadvertentcontact between the pattern rib 64 and the platen roll 30, and thusminimizes (if not eliminates) the risk of damaging the rib 64.

FIG. 7 shows the pattern roll 28 according to this invention inrelationship to a planar projection thereof as shown in FIG. 8. Acomparison between FIGS. 4 and 8 will reveal that the pattern rib 60 ofpattern roll 28 forms a negative image of the tapered edge 18, with thepattern roll 28 itself being a negative image of the mat preforms 40which are formed thereby.

As is perhaps more clearly seen in FIG. 8, the pattern rib 60 iscomprised of a number of circumferential segments 60a (i.e., segmentswhich conform to a cylindrical surface whose generatrices are equallyradially spaced from the longitudinal axis 70 of the roll 28) and anumber of longitudinal segments 60b (i.e., segments which extendparallel to the axis 70 of roll 28). Continuity of adjacentcircumferential and longitudinal segments 60a and 60b, respectively, isachieved via outside and inside radii transition segments 60c and 60d,respectively. By the term "outside radius segment" is meant a segment ofpattern rib 60 having a radius bend whose geometric center lies withinthe interior region 62 of roll 28. Conversely, by the term "insideradius segment" is meant a segment of pattern rib 60 having a radiusbend whose geometric center lies within the lateral region 65 of roll28.

As can be appreciated, predetermined combinations of circumferential,longitudinal, inside radius and outside radius segments will formdesired peripheral boundaries, which in the embodiment shown in theaccompanying FIGURES, just happens to be in the peripheral outline ofthe chair mat 10 described previously. Other peripheral outlines are ofcourse possible without departing from the present invention. Forexample, a rectangular mat could be formed by providing opposing pairsof circumferential and longitudinal segments with adjacent ones beingjoined by means of four outside radius segments. Suffice it to say here,that the product designer can use the concepts of the present inventionto provide virtually any desired peripheral outline.

Accompanying FIG. 9 shows in greater detail the pattern rib 60 and thebase roll 72 in a disassembled view for ease of description--it beingunderstood that when assembled the pattern rib 60 and the base roll 72collectively form the pattern roll 28. The base roll 72 includes acontinuous groove 74 machined into its exterior surface to asubstantially constant depth dimension d_(g). It will be observed thatthe groove 74 establishes circumferential and longitudinal sections 74aand 74b, respectively, continuously joined to one another by outside andinside radii sections 74c and 74d, respectively, in correspondence withthe segments 64a-64d.

The groove is most conveniently formed by a conventional four (or more)axis, numerically controlled milling machine having a flat end mill. Theend mill is maintained stationary while the roll is mounted on asuitable controllably movable table. Thus, under controlled movements(which may be accomplished by means of a microprocessor preprogrammedwith the desired table movements), the table will present the roll 72 tothe end mill so that the groove 74 may be formed.

The pattern rib 60 is, like groove 74, formed by milling using a four(or more) axis, numerically controlled milling machine by removingunwanted regions thereof (i.e., those regions not shown in solid line inFIG. 9) from a solid tubular sleeve cylinder 76 having an insidediameter D_(i). It will be appreciated that the inside diameter D_(i) ischosen so that it is substantially equal to the outside diameter D_(o)of roll 72 less twice the groove depth d_(g) (i.e., D_(i) =D_(o)-2d_(g)).

In practice, the tubular cylinder 76 is rigidly telescopically mounted(i.e., sleeved) upon a mandrel roll (not shown) by means of suitablebolts extending through both the unwanted regions of the cylinder 76 andthat region which will remain after milling (i.e., the pattern rib 60).Preferably, a number of jacking bolts connect the region of cylinder 76which will eventually form the pattern rib 60 to the mandrel roll (notshown) so as to allow for repeated assembly and disassembly of thepattern rib 60 relative to the groove 74. Milling may then proceed bymounting the mandrel roll/cylinder 76 onto the movable table of themilling machine and then milling the interior and exterior peripheriesof the pattern rib 60. Thereafter, the unwanted portions of the cylinder76 may be removed (as by removing the bolts securing them to the mandrelroll) to thereby leave the pattern rib 60 on the mandrel roll.

After removing the unwanted portions of the cylinder 76 from the mandrelroll, a planar beveled interior edge 64 of the pattern rib 60 may thenbe milled, again using a four (or more) axis milling machine underpreprogrammed computer numerical control. Important to the presentinvention is that the length of the planar beveled interior edge 64(i.e., as measured in a plane parallel to the plane of the edge 64) issubstantially equivalent to the length L of the edge 18 on mat 10 whichwill be formed thereby (see FIG. 2). However, as will be explained ingreater detail below, it is critically important that different angularrelationships exist as between the edge 19 on the circumferential andlongitudinal segments 60a and 60b, respectively, and the exteriorsurface of the roll 74.

The pattern rib 60 in its unitary continuous configuration as shown inFIG. 9 cannot, of course, be positioned physically into the groove 74 inone piece (i.e., since the inside diameter D_(i) of the one-piecepattern rib 60 is less than the outside diameter D_(o) of the roll 72).Therefore, it is necessary to provide a number (n) of discrete sectionsof pattern rib 60 which can most conveniently be accomplished by cuttingthrough the cross-section of the pattern rib 60. Preferably, no onediscrete section of pattern rib 60 will have more than one of theoutside and/or inside radii segments 60c and/or 60_(d), respectively.

It will be appreciated that cutting through the one-piece pattern rib 60so as to form a number (n) of sections thereof will result in the lossof material of rib 60 to the extent of the thickness (as measured in theperimetrical direction) of the rib 60. For this reason, the one-piecerib 60 is somewhat "longer" perimetrically in its as-milled condition(i.e., prior to forming discrete sections thereof) as compared to theperimetrical "length" of the groove 74. That is, the milling of thecylinder 76 is accomplished so as to compensate for the later materialremoval due to sectioning of the pattern rib 60. Hence, the as-milledperimetrical "length" P_(r) of the rib 60 is greater than acorresponding perimetrical "length" P_(g) of the groove 74 by an amountof the number (n) of sections of pattern rib 60 times the materialthickness "t" removed during sectioning (i.e., P_(g) =P_(r) -nt) In thismanner, the eventual perimetrical "length" of the pattern rib 60sections will be substantially equivalent to the perimetrical "length"of the groove 74 when the segments are assembled therein.

FIG. 10 is a cross-sectional view of a circumferential segment 60a ofpattern rib 60 as taken along line 10--10 in FIG. 8, but is alsoschematically representative of the longitudinal segment 60b of patternrib 60 (except for the differential angular relationships of beveledinterior edge 64 of the circumferential and longitudinal segments 60aand 60b, respectively, to be described below). As is seen, the segment60a is seated within the groove 74 formed in roll 72 so that it projectsabove the interior and lateral surfaces 62 and 65, respectively, of theroll 72. It will be noted that the planar interior edge 64 of section60a is of a length L (i.e., substantially equal to the length L of edge18 of mat 10 to be formed thereby) and intercepts a plane tangent tointerior surface 62 of roll 72 at a point 80. Thus, an uninterruptedV-shaped transition is present from the surface 62 of roll 72 to theplanar beveled interior edge 64 of pattern rib 60.

Of course, the edge 64 associated with the circumferential rib segments62a is itself circumferentially disposed about the axis 70 of roll72--that is, the edge 64 of the circumferential segments 60a representsa conical segment. However, at any plane coincident with axis 70 passingtransversely through the circumferential rib segments 60a, the edge 64is planar in cross-sectional profile. Because of this, the edge 64formed on the circumferential segments 60a of pattern rib 60 will, forease of reference, be described as cross-sectionally "planar". Thebeveled interior edge 64 formed on the longitudinal segments 60b, on theother hand, is truly planar--that is, does not curve about the axis 70of roll 72 but rather represents a chordal plane passing through thebase roll 72. Thus, at any plane passing perpendicularly through theaxis 70, the cross-sectional profile of the edge 64 formed on thelongitudinal segments 60b will also be cross-sectionally planar.

The pattern rib 60 is physically secured to the roll 72 via a number ofbolts, one of which is shown in FIG. 10 by reference numeral 80. A rigidplug 82 is press-fitted into the rib 60 over the head of the bolt 80 soas to present a smooth upper surface 84 laterally of thecross-sectionally beveled surface 64.

FIG. 11 schematically shows the geometry of the longitudinal groovesection 74b. As is seen, since the groove section 74b extendslongitudinally (i.e., parallel) to the axis 70 of roll 72, the surfaces62 and 65 will, in cross-section, appear curved. The groove depth d_(g)of the groove section 74b will thus be measured from a line (i.e.,extending out of the plane of FIG. 11 at point 83) formed by theintersection of a reference plane 84 and a longitudinal midplane 85 ofthe groove 74b (i.e., a plane which intersects the axis 70 of the roll72 and laterally bisects the groove 74b) tangent to the cylindricalexterior surface of roll 72. It will be observed that the tangent plane84 also represents the surfaces 62 and 64 of roll 72 for circumferentialgroove section 74a as viewed in cross-section. Thus, the groove depthd_(g) of the groove 74 will be substantially constant as between thecircumferential and longitudinal groove sections 74a and 74b,respectively (see FIG. 13).

It will also be observed in FIG. 11 that the bottom surface 87 of thegroove section 74b is flat and thus establishes a plane which isparallel to the tangent reference plane 84 but separated therefrom bythe groove depth d_(g). Similarly, the bottom surface 87 of thecircumferential groove section 74a will, in cross-section, appear planarand will be parallel to a plane tangent to the surfaces 62 and 65 ofroll 72. However, it is to be understood that the bottom surface 87 ofthe circumferential groove section 74a conforms to the generatrices of aright cylinder radially spaced from the axis 70 of roll 72 by adimension equal to the outside diameter D_(o) of roll 72 less the groovedepth d_(g).

A schematic cross-sectional representation of a longitudinal rib segment60b is shown in accompanying FIG. 12. As is seen the thickness t_(r) ofthe longitudinal rib section 60b (as measured between the bottom surface60b' of segment 60b and upper surface 82b) is substantially equal to theradial thickness t_(c) of the cylindrical sleeve 76. Therefore, opposingarcuate tangs 60b₁ and 69b₂ are removed via milling so as to establish aplanar bottom surface 60b'. Similarly, a region 60b₃ is removed viamilling so as to establish a planar upper surface 82b.

Important to the present invention, the beveled surfaces 64 associatedwith the circumferential and longitudinal rib segments 60a and 60b,respectively, must be differentially angularly oriented with respect tothe exterior surface of roll 72 as will now be discussed with referenceto FIG. 13. FIG. 13 is a composite view, for ease of understanding,showing the circumferential and longitudinal rib segments 60a and 60b,respectively, superimposed onto one another in relationship to thesurfaces 62 and 65 of roll 72.

As will be observed, the intersection at point 80 of the beveled surface64 associated with the circumferential segments 60a forms an angle A₁with the tangent plane 84 (i.e., in the context of rib segment 60a,plane 84 is the same as the cross-sectional plane established by thesurfaces 62 and 65). Moreover, the cross-sectional profile of thesurface 64 associated with the rib segment 60a and the surface 62 ofroll 72 forms an angle A₁ which is the same angle A₁ formed by theintersection of the plane of edge 18 and the top surface 16 of mat 19(see FIG. 2).

The surface 64 associated with the longitudinal rib segments 60b,however, must intersect the tangent line 80' (i.e., a line extending outof the plane of FIG. 12 at point 80') so as to provide an uninterruptedV-shaped transition between the surface 62 of roll 72 and the beveledsurface 64 of rib segments 60b. That is, since the surface 62 "fallsaway" from the longitudinal midplane 85 of rib segment 60b incross-section (i.e., due to the cylindricity of surface 62), the line ofintersection 80' between the surface 64 of rib segment 60b and thesurface 62 will be displaced radially towards the axis 70 of roll 72 ascompared to the intersection between the surface 64 of thecircumferential segments 60a and the surface 62.

Therefore, it has been discovered that, in order to maintain a constantdimension L for surfaces associated with both the circumferential andlongitudinal rib segments 60a and 60b, respectively, the angle A₂ formedby the intersection between the surface 64 associated with the ribsegment 60b and the tangent plane 84 must be greater than the angle A₁formed between the surface 64 associated with the circumferential ribsegments 60a and a similar plane 84. It might be expected that such anangular difference between angles A₁ and A₂ would translate into adifference in the base length L_(b) (see FIG. 2) of the tapered edge 18about the periphery of mat 10. However, contrary to this expectation, ithas been found that the base length L_(b) is substantially constantabout the mat's periphery. Moreover, this constant dimensioning of theperipheral edge 18 results in little or no distortion thereof.

Because of the angular differential as between angles A₁ and A₂discussed above, it is also necessary according to this invention toprovide a transition surface 64' for the outside and inside radii ribsegments 60c and 60d, respectively. A two-dimensional representation ofan outside radius segment 60c and a portion of a longitudinal ribsegment 60b is shown in accompanying FIG. 14. In two dimensions, it willbe observed that the line 64" of intersection with the exterior surfaceof roll 72 for the transition surface 64' "drops" radially towards theaxis 70 of the roll 72 between intersection point 80 and intersectionline 80'.

The angle formed by the surface 64' and the intersection line 64" asviewed in planes passing radially cross-sectionally through the radiussegment 60c will therefore continuously gradually increase from angle A₁to angle A₂ --that is, as one views the surface 64' sequentially fromradial cross-sectional planes near the terminal end of onecircumferential rib segment 60a to the beginning end of a longitudinalrib segment 60b. For example, as viewed in radial cross-sectional planespassing through the segment 60c, the angle formed by transition surface64' near intersection point 80 will be slightly larger than angle A₁,whereas a radial cross-sectional planes passing through the segment 60cnear the intersection line 80', the formed angle will be slightly lessthan angle A₂, with gradual intermediate angles formed therebetween. Inorder to more easily facilitate insertion of the outside radius segments60_(c), an exterior region 86 is removed about the radius bend ofsegments 60c as is shown in FIG. 14.

FIG. 15 shows one possible cross-sectional profile which may be providedfor rib 60. As is seen, the cross-section profile of rib 60 includessurface 164 (which is a negative image of the tapered edge 18 of mat 10)which slopes upwardly and outwardly away from the recessed region 62.Surface 164 terminates in a converging pair of edge-forming surfaces166, 167 which project toward the external cylindrical surface 30a ofplaten roll 30 but establish a small gap of a dimension D therebetween.The edge forming surfaces 166, 167 thus establish the lateral-mostextent of tapered edge 18.

Gap "D" in the continuous in-line extrusion process of the presentinvention permits the molten thermoplastic material to be compressed inthe volumetric portion 168 (i.e. that discrete volumetric portionestablished at the nip 26 between the recessed region 62/surface 64 andthe opposing surface 30a of platen roll 30) and flow through gap D tothe lateral waste region 170 (i.e., that region established betweensurface portion 65 of pattern roll 28 and surface 30a of platen roll 30in opposition therewith). Thus, gap "D" defines an escape route forexcess molten thermoplastic extruded into nip 26 and compressed (i.e.,molten) between rolls 28 and 30. This compressive force, in turn,permits the surface 164 to, in effect, mold in a continuous manner thetapered edges 18 of mat 10. However, since thermoplastic material willbe present in gap D between the edge forming surfaces 166, 167 of rib60, the mats 10 will be connected to the waste region 42--that is, themat preforms 40 will be formed and connected to the waste regions 42 yetwill be in a condition where they can easily be removed therefrom as hasbeen discussed above.

An alternate possible cross-sectional profile of rib 60 is shown inaccompanying FIG. 16. As is seen, the profile of rib 60 shown in FIG. 16is identical to that shown in FIG. 15 with the exception being that anextension surface 172 projects laterally of the edge forming surfaces166, 167 (i.e. projects into the waste region 68). The projectionsurface 172 thus permits suitable bolts (not shown) or like securingmeans to pass vertically therethrough so as to insure rigid couplingbetween the rib 60 and the pattern roll 28.

Although reference has been made above to the formation of beveledperipheral edges on plastic products, it will be understood that suchreference is merely a particularly preferred use of the pattern rolls ofthis invention. Suffice it to say here, that those in the art may findother beneficial uses for the pattern rolls of the present invention soas to form beveled edges on products made from a variety of materials,e.g., the shaping of metal products, leather goods, and/or othermalleable materials.

Therefore, while the invention has been described in connection withwhat is presently considered to be the most practical and preferredembodiments, it is to be understood that the invention is not to belimited to these disclosed embodiments. Instead, the invention isintended to cover various modifications and equivalent arrangementsincluded within the spirit and scope of the appended claims.

What is claimed is:
 1. A method of fabricating a pattern roll which isadapted to form first and second beveled peripheral edge portions ofsubstantially constant geometry on an article by passing a preform ofthe article between the pattern roll and a platen surface, said methodcomprising the steps of:(a) forming at least one continuous recessedgroove of a depth dimension d_(g) in a cylindrical surface of a baseroll having a predetermined outside diameter D_(o), the groove having anumber of circumferentially extending sections and a number oflongitudinally extending sections joined to one another such that thegroove formed in the cylindrical surface of the roll, when projectedonto a planar surface, has a geometric configuration which establishes aperipheral outline of said article; (b) forming, from a rigidcylindrical sleeve having an internal diameter D_(i) less than saiddiameter D_(o) of said base roll and a radial thickness t_(c) greaterthan said groove depth d_(g), a number of unitarily joinedcircumferential and longitudinal rib segments by removing unwantedportions of said cylindrical sleeve so that said number of unitarilyjoined circumferential and longitudinal rib segments remain; (c) formingbeveled surfaces on said circumferential and longitudinal rib segmentssuch that said beveled surfaces of said circumferential rib segments areformed at an angle A₁, while said beveled surfaces of said longitudinalsegments are formed at an angle A₂ greater than angle A₁ ; and (d)rigidly positioning said circumferential and longitudinal rib segmentsin respective circumferential and longitudinal grooved sections, wherebysaid first and second beveled peripheral edge portions of substantiallyconstant geometry may be formed by said circumferential and longitudinalrig segments, respectively.
 2. A method as in claim 1, wherein said step(a) of forming at least one continuous raised groove includes forming anumber of radius groove sections joining adjacent ones of saidcircumferential and longitudinal groove sections, and said step (b) offorming a number of unitarily joined circumferential and longitudinalrib segments includes forming from said cylindrical sleeve, a number ofradius rib segments to be rigidly received within respective ones ofsaid radius groove sections.
 3. A method as in claim 2, furthercomprising the step of forming a beveled surface on said number ofradius rib segments such that said beveled surface thereof presents asmooth transition between said angles A₁ and A₂.
 4. A method as in claim3, further comprising sectioning said unitarily formed circumferentialand longitudinal rib segments to establish a number of discrete patternrib segments thereof.
 5. A method as in claim 4 wherein at least one ofsaid discrete pattern rib segments unitarily includes a circumferentialrib segment and a radius rib segment.
 6. A method as in claim 4, whereinat least one of said discrete pattern rib segments unitarily includes alongitudinal rib segment and a radius rib segment.
 7. A method as inclaim 4, wherein said step of sectioning said unitarily formedcircumferential and longitudinal rib segments is practiced before saidstep (d) of rigidly positioning said circumferential and longitudinalrib segments.
 8. A method as in claim 1, further comprising the step ofremoving arcuate tang portions from a bottom of said longitudinal ribsegments.
 9. A method as in claim 4, further comprising relieving anexternal radius section from predetermined ones of said radius ribsegments.
 10. A method as in claim 4 wherein a perimetrical dimension Prof said unitarily joined circumferential and longitudinal rib segmentsis greater than a perimetrical dimension Pg of said circumferentiallyand longitudinally extending groove sections prior to sectioning of saidrib segments.
 11. A method of fabricating a pattern roll which isadapted to form a beveled edge portion of substantially constantgeometry about a periphery of an article, said method comprising thesteps of:(a) forming on a cylindrical base roll at least onecircumferentially extending recessed groove and at least onelongitudinally extending recessed groove relative to a central axis ofthe base roll; (b) forming at least one circumferential rib segment andat least one longitudinally rib segment from a rigid cylindrical sleeveby removing unwanted regions of said sleeve so that remaining regionsthereof form said at least one circumferential and longitudinal ribsegments; (c) forming a beveled surface on each of said at least onecircumferential rib segment and said at least one longitudinal ribsegment such that the beveled surface on said at least onecircumferential segment is formed at an angle A₁ which is less than anangle A₂ formed by the beveled surface on said at least one longitudinalrib section; and then (d) rigidly securing said at least onecircumferential and longitudinal rig segments within said at least onecircumferentially and longitudinally extending groove sections,respectively, whereby said beveled edge portion of substantiallyconstant geometry about the periphery of said article may be formed bysaid beveled surfaces on said at least one circumferential andlongitudinal rib segments.
 12. A method as in claim 11, wherein saidstep (a) of forming at least one continuous raised groove includesforming a number of radius groove sections joining adjacent ones of saidcircumferential and longitudinal groove sections, and said step (b) offorming a number of unitarily joined circumferential and longitudinalrib segments includes forming from said cylindrical sleeve, a number ofradius rib segments to be rigidly received within respective ones ofsaid radius groove sections.
 13. A method as in claim 12, furthercomprising the step of forming a beveled surface on said number ofradius rib segments such that said beveled surface thereof presents asmooth transition between said angles A₁ and A₂.
 14. A method as inclaim 13, further comprising sectioning said unitarily formedcircumferential and longitudinal rib segments to establish a number ofdiscrete pattern rib segments thereof.
 15. A method as in claim 14,wherein at least one of said discrete pattern rib segments unitarilyincludes a circumferential rib segment and a radius rib segment.
 16. Amethod as in claim 14, wherein at least one of said discrete pattern ribsegments unitarily includes a longitudinal rib segment and a radius ribsegment.
 17. A method as in claim 14, wherein said step of sectioningsaid unitarily formed circumferential and longitudinal rib segments ispracticed before said step (d) of rigidly positioning saidcircumferential and longitudinal rib segments.
 18. A method as in claim11, further comprising the step of removing arcuate tang portions from abottom of said longitudinal rib segments.
 19. A method as in claim 14,further comprising relieving an external radius section frompredetermined ones of said radius rib segments.